Ninety-seven per cent of right-handed (RH) individuals develop speech and language processing in the left (dominant) hemisphere of the brain, while the minor hemisphere controls emotional behavior. However, this correlation fails in LH (left-handed) individuals; 70% are left-brain dominant and 30% are right-brain dominant. The reason for this complex correlation of handedness with brain lateralization has been the key unanswered question for brain development. We have speculated that a hypothetical gene, RGHT, functions to specify left-brain dominance resulting in developing the right-handed preference. To test these ideas experimentally, we have been collecting blood samples and cheek swabs from specific families with the aim to genetically map the hypothesized RGHT gene. We have collected enough samples and the next stage is to use these samples for mapping by the sib-pair method. We have published our random recessive model in which individuals with the nonfunctional recessive allele on both homologs have a 50:50 chance of either being RH or LH.